Overexpression of arginase in Arabidopsis thaliana influences defence responses against Botrytis cinerea

Abstract

Arabidopsis possesses two arginase-encoding genes, ARGAH1 and ARGAH2, catalysing the catabolism of arginine into ornithine and urea. Arginine and ornithine are both precursors for polyamine biosynthetic pathways. We observed an accumulation of ARGAH2 mRNA in Arabidopsis upon inoculation with the necrotrophic pathogen Botrytis cinerea. Transgenic lines displaying either overexpression of ARGAH2 or simultaneous silencing of both Arabidopsis arginase-encoding genes were created and their resistance to B. cinerea infection evaluated. Overexpression of arginase resulted in changes in amino acid accumulation, while polyamine levels remained largely unaffected. Silencing lines were affected in both amino acid and putrescine accumulation. Arabidopsis plants overexpressing the arginase gene were less susceptible to B. cinerea, whereas silencing lines remained as susceptible as the wild type. We discuss how arginase might interact with plant defence mechanisms. These results provide new insights into amino acid metabolic changes under stress.

In vivo role ofArabidopsisarginase in arginine metabolism and abiotic stress response

“…17 Some stress factors might share the activation of stress responsive pathway in the plant, characterized by arginine concentration per g fresh weight (FW), AtARGAHs knockout and overexpressing lines showed significantly less relative arginine (% of total free amino acids) than that of wild type. 5 All these results were consistent with what Flores et al (2008) and Brauc et al (2012) reported. 2,3 It is reasonable that all AtARGAHs overexpressing lines showed decreased relative arginine, indicating a direct effect of AtARGAHs on arginine pools.…”

“…1,4,17 As shown in Figure 1, manipulating the expression of AtARGAHs supplied a good version to investigate the link between NO and polyamines, especially in plant responses to abiotic stress. [2][3][4][5] Our previous research together with other published data confirmed that proper levels of NO might be necessary and beneficial for plants in response to both abiotic stress and disease resistance. [6][7][8][9][10][11]13,14 As to polyamines, overexpression of several polyamine metabolism genes including ADC and SPMS resulted in increased polyamines and enhanced abiotic stress tolerance, while knockdown of these genes had the opposite results.…”

“…[2][3][4][5] If arginase expression was modulated, the direct insight was to examine the arginine accumulation. Although changes of AtARGAHs expression had no significant effect on upstream ArticLe AddenduM the production of nitrogen species and reactive oxygen species (ROS).…”

“…[1][2][3][4][5] As shown in Figure 1, arginase (also known as ARGAH in Arabidopsis) is responsible for catalyze of arginine to ornithine and urea, and arginine decarboxylase (ADC) can metabolize arginine to agmatine and further to polyamines including putrescine, spermidine, spermine, etc. 2,3,5 Additionally, although nitric oxide synthase (NOS) has not been cloned in higher plants, similar NOS activity of animals has been detected in many plant species by many research groups. [6][7][8][9][10][11] And it has been confirmed that NO might be generated primarily during the conversion of arginine to citrulline by the NOS, especially in responses to several biotic and abiotic stresses.…”

“…[6][7][8][9][10][11] Previous research indicated that knockout of Arabidopsis arginase gene resulted in increased NO accumulation, 2 and overexpression of AtARGAH2 conferred increased tolerance to Botrytis cinerea and enhanced callus development during clubroot infection. 3,12 Recently, we investigated the influence of manipulation of AtARGAHs expression on arginine metabolism, as well as plant responses to abiotic stresses including water deficit, salt and freezing. …”